The addition of flame retardants to polymer resins during processing is well known. Flame-retardant additives can be categorized in general by three basic mechanisms. Vapor phase flame-retardants work in the vapor phase by free radical flame poisoning, which removes active free radicals that promote further exothermic reactions. The ubiquitous halogenated flame-retardants are believed to function as vapor phase flame-retardants. Often, these compounds are used along with synergists, e.g., antimony synergists. Condensed-phase flame-retardants promote the formation of char in the solid phase to form an insulating layer which protects the flammable substrate from the fire and reduces the emission of volatile flammable gases into the fire. Many phosphorus and silicone-based flame retardants are believed to function as condensed-phase flame-retardants. Heat sink flame-retardants work via endothermic reactions by releasing water and/or carbon dioxide, which quench the fire.
Halogenated organic compounds, including oligomeric and polymeric materials are widely used and are highly effective flame retardant additives for polymer resins. Examples of commercially available brominated flame retardants include tetrabromobisphenol A, bis(2,3-dibromopropyl ether), hexabromocyclododecane, tris(tribromoneopenyl)phosphate, poly(pentabromobenzyl acrylate), decabromodiphenyl oxide, tris(tribromophenyl)cyanurate, tris-dibromopropyl isocyanurate, brominated polystyrenes and poly(bromostyrenes).
In order to meet high flame retardance standards in thermoplastics, for example, the UL-94 V-0 standard, halogenated flame retardants are generally blended with a synergist, most commonly antimony trioxide (ATO). However, for compliance with voluntary environmental standards, the use of antimony trioxide has been restricted due to its chemical hazard classification. Also, the use of synergists can lead to challenges in coloring, increased cost, and can in some cases negatively impact polymer properties. It would therefore be highly desirable to limit or eliminate antimony compounds and similar synergists from polymer compositions.
Thermoplastic polyphenylene oxide resins, such as polymers of 2,6-dimethylphenol, are commercially available and are most often encountered as polymer additives or as part of a polymer blend, e.g., polyamide blends and high impact polystyrene, i.e., HIPS.
Polyphenylene ethers (PPE), also called polyphenylene oxides (PPO), are inherently flame resistant. U.S. Pat. No. 4,888,370 discloses the use of PPO as a flame retardant additive in polyamide. U.S. Published Patent Application No. 2010/0292376 discloses the use of polyphenylene ethers as a flame retardant adjuvant in polymer resins comprising benzylic phosphine oxide flame retardants.
PPOs are often not very effective as flame retardants on their own and are more often added to polymer resins to improve physical properties such as dimensional stability, mechanical and dielectric strength etc. In many such applications where PPO is used, other flame retardant additives or packages, such as phosphinates, halogenated flame retardants metal synergists etc, are incorporated when flame retardance is required.
U.S. Published Patent Application No. 2006/0167143 discloses a composition which comprises a compatibilized poly(arylene ether)/polyamide blend, a phosphinate flame retardant and a flame retardant augment selected from the group consisting of melamine polyphosphate, zinc borate, low melting glass and talc.
U.S. Pat. No. 420,393, discloses a self-extinguishing thermoplastic molding composition, such as rubber-modified high-impact polystyrene, with improved mechanical properties and good flame resistance comprising styrene resin, polyphenylene ether resin, a halogenated aromatic frame retardant compound, an antimony containing compound and an additive selected from the group consisting of polyesters and, polyethylene.
U.S. Pat. No. 4,024,093 discloses a flame retardant thermoplastic molding composition comprising polyphenylene ether resin, a vinyl aromatic resin, an aromatic halogenated flame retardant; and a flame retardant amount of an organic iron. U.S. Pat. No. 5,143,955 discloses a composition comprising a polyphenylene ether resin, e.g., poly(2,6-dimethyl-1,4-phenylene)ether, a high impact polystyrene resin, a brominated aromatic flame retardant and a high molecular weight polystyrene resin.
U.S. Pat. No. 7,816,430 discloses a curable composition for a printed wiring board comprising a cyanate ester compound and/or a prepolymer thereof, a specific epoxy resin, a monovalent phenol and a polyphenylene ether resin. The composition can further comprise a brominated flame retardant. Among the list of possible flame retardants is brominated polyphenylene ether.
Aryloxy carbonates, such as the widely used bis-phenol A polycarbonate (BPA-PC) and similar materials, are commercially available thermoplastic polymers. PCs may be used as the sole or predominate polymer in a plastic article, and also find use in various blends, for example, PC-ABS blends. Polycarbonates are not typically associated with flame retardant activity.
Halogenated polyphenyl ethers are known flame retardants. U.S. Pat. No. 3,760,003 discloses compounds of the formula
wherein each X is independently Cl or Br, each m is independently a number from 0 to 5, p is a number from 0 to 4, and n is a number from 1 to 5, which are useful as flame retardants in polymer resins such as polyester, polystyrene and ABS. Published US Pat. Appl. 2011/0040003 and 20110184107, and copending U.S. application Ser. No. 13/248,387, published as US 20120065297, the disclosures of which are incorporated herein by reference, disclose mixtures of brominated aryl ether oligomers as flame retardants.
It has been found that certain of these halogenated poly ether flame retardants can interact with synergists, adjuvants and other materials differently than many similar halogenated aromatic flame retardants. Very surprising is the discovery that the halogenated polyethers having at least three halogenated aromatic rings are more effective than decabromodiphenyl ether when used in combination with phenoxy containing materials such as polyphenylene ethers, aryl carbonates and the like, e.g., non-halogenated PPOs such as polymers of 2,6-dimethylphenol and aromatic polycarbonates.
As a result, it has now been found that compositions comprising a mixture of halogenated polyethers, wherein the majority of the ethers comprise at least three halogenated aromatic rings, and non-brominated polypheneylene oxide ethers or aryl carbonates can be prepared that meet the UL-94 V-0 standard for flame retardancy without the addition of metal based synergists. Other brominated aromatic flame retardants tested do not achieve the V-O standard unless a metal based synergist like antimony trioxide is added. The present invention allows for increased flexibility in formulating polymer compositions containing no ATO, or reduced levels of ATO, with excellent flame retardancy and excellent physical characteristics.